The present invention relates to the semiconductor industry in general, and to an apparatus for monitoring wafers and process control in the semiconductor processing and a method for use thereof, in particular.
The current trends of shrinking dimensions in the semiconductors industry and the dynamic nature of the processes involved in the semiconductor manufacturing, increase the need for accurate diagnostic tools, capable of providing real time measurements for short time to-respond feedback loops, such as closed loop control and feed forward control. Such stringent requirements cannot be obtained by off-line (xe2x80x9cstand alonexe2x80x9d) measuring systems, which do not provide a real time response. Inspection and measuring by such systems, however precise and accurate they are, slow-down the manufacturing process and consume valuable time and clean room space. On the other hand, in-situ detection devices such as end-point detection devices, which are used at different stages of the production line, although they provide real-time monitoring, their performance is not accurate enough. Such devices are exposed to the conditions in the active area of the production line, thus the data obtained by them is rather an averaging over a relatively large area and they cannot provide mapping capabilities.
This situation enhanced the development of a fundamental solution by means of integrated monitoring and process control, i.e., physical implementation of monitoring tools, with full metrology capabilities, within the production line in the semiconductor fabrication plant. (Dishon, G., Finarov, M., Kipper, R. (1997) Monitoring choices of CMP planarization process, 2nd International CMP planarization conference, February 13-14, Santa Clara, Calif.)
The terms xe2x80x9cintegrated apparatusxe2x80x9d or xe2x80x9cintegrated devicexe2x80x9d as used in the present invention refers to an apparatus that is physically installed inside the processing equipment or is attached to it and is dedicated to a specific process. Wafers are transferred to said apparatus by the same robot which serves the processing equipment.
Integrated devices should be considered from several aspects and meet specific requirements in order to become real and feasible:
(a) Small footprintxe2x80x94an integrated device should have as small footprint as possible in order to be physically installed inside the Processing Equipment (hereinafter called PE), e.g., inside the Chemical Vapor Deposition (hereinafter called CVD) equipment, inside the Chemical Mechanical Polishing (hereinafter called CMP) polisher or inside the photocluster equipment;
(b) Separation of the measuring unit from the PE environment, e.g., using sealed enclosure. This is aimed at two objectives:
(I) Cleanlinessxe2x80x94measuring unit must not interfere in any way with the operation of the PE or introduce any potential risk for contamination;
(II) To enable the application of certain conditions inside the integrated apparatus, such as pressurized gases in the CMP equipment (in order to prevent water vapor from penetrating the apparatus);
(c) Maintaining a stationary wafer during measurement in order to minimize system""s footprint and to exclude extra wafer handling;
(d) High speed measuring unit (e.g., fast positioning, autofocusing and measurement);
(e) Means to directly respond to a certain cause with the correct straightforward correction action.
(f) Easy and quick maintenance by simple replacement of each functioning unit (component).
(g) Having the option to be bypassed by the production process and to operate at off-line mode.
In addition to the aforementioned specific design requirements, integrated device should have other general functions as described hereinafter.
Reference is made to FIG. 1, prior art, which generally illustrates an integrated apparatus which measures the thickness of thin films on the surface of a silicon wafer (the metrology device known as Integrated Thickness Monitoring systemxe2x80x94ITM NovaScan 210, commercially available from Nova measuring instruments Ltd., Rehovot, Israel). The prior art will be described using this metrology device. In general, the known metrology apparatus of FIG. 1 comprises an optical measurement unit (MU) 1, an external light source 10 and a control unit (CU) 2, which controls the movement and image acquisition of the optical measurement system 1 as well as the operation of the external light source 10. The optical measurement system xe2x80x98seesxe2x80x99 the wafer through an optical window 3.
Optical measurement system 1 typically comprises an optical unit 4, whose optical path is shown in detail in FIG. 2, a translation system 5 capable of allocating measurement at any point on the wafer w, such as an X-Y stage, and data and image processing unit 6 forming part of the control unit 2.
The optical path for the exemplary apparatus is illustrated in FIG. 2 and is described hereinafter. The optical unit comprises an external (to the MU 1) white light source 10, an optic fiber 11, a condenser 12, which directs the light onto a beam splitter 13, a focusing target 25, a tube lens 14, a translatable objective 15, an optical window 3 and the wafer""s plan w. Behind the beam splitter 13 are located a pinhole mirror 16, a relay lens 17 and a CCD camera 18. Behind the pinhole mirror 16 there is another relay lens 19, a mirror 20 and a spectrophotometer 21. For the apparatus described here, only the objective 15 is translated, parallel to the wafer""s plan w.
A light beam 22 emanates from the external light source 10, is conveyed to the MU 1 by fiber optic 11. It enters the MU 1, to the condenser 12 till beam splitter 13 which deflects it toward the wafer w, via lenses 14 and 15 (mirrors which serve as well to convey light beam 22 are not shown) The reflected light beam (not labeled) is transmitted by lenses 14 and 15, passes through beam splitter 13 and is deflected by pinhole mirror 16 to the CCD camera 18 where the image acquisition takes place. The portion of the light beam, which passes through the pinhole in the pinhole mirror 16, reaches the spectrophotometer 21. The focusing target 25 is any high contrast object, such as a metallic pattern on a glass substrate. The pattern can be any easily identifiable pattern, such as a contrast edge, a grid, etc.
The main two functions of the optical unit 4 are the positioning (including focusing, image acquisition and image processing) channel 100 and the measuring (including illumination and detection) channel 200. The positioning channel 100 is aimed at identifying the exact location of the wafer w and the specific sites on the wafer w where measurements have to be done. Autofocusing using, among other things, focusing target 25, is performed according to any method known in the art. Such a method based on the patterned features on the wafers is disclosed in U.S. Pat. No. 5,604,344. After the positioning and autofocusing are done, the objective 15 is located above the predetermined location on the wafer w. Now, a measurement is conducted by the measuring channel 200. It should be noted that the positioning channel 100 and the measuring channel 200 are partly composed of the same optical elements as shown in FIG. 2, especially with respect to the moving optical head which is the objective 15 in this case. This overlap is feasible, mainly because both channels 100 and 200 in the ITM NovaScan 210 use almost the same spectral range. A direct result of this situation is that single optical window 3 is capable to serve both channels.
However, another situation is when an integrated measurement device uses different wavelengths for the positioning channel and for the measuring channel, or when optical measurements are required at more than one spectral range. For example, a method for layer composition measurements and contamination analysis during the CVD process is conducted by infrared optical assembly which cannot be used for the positioning channel 100.
Therefore, with respect to applications when different wavelengths are used for positioning and for measurements or when measurements at different spectral ranges are required, a new shortcoming of the common integrated devices arises: due to optics limitations, both positioning channel 100 and measuring channel 200 cannot use the same optical elements and the optical window 3 cannot serve both channels, as known to a man skilled in the art. With respect to the known ITM NovaScan 210 presented above, optical window 3 designed for positioning channel 100 and operation under visible light conditions, cannot serve UV, Infrared or X-rays measuring. Moreover, recalling the specific requirements for integrated device, this problem cannot be solved by installing two different optical windows with similar dimensions to those of optical window 3 due to footprint limitations. Alternatively, a permanent omission of the optical window 3 is not practical because of the requirement to separate the MU 1 from its environment.
Therefore, the objectives of the present invention is to overcome the aforementioned limitations:
1) To provide an integrated apparatus for monitoring and process control under conditions where different spectral ranges are used for positioning, measurement, mapping and any other operation performed by the apparatus or any combination of such operations.
2) To provide specifically an integrated apparatus for monitoring layers thickness and layers composition and for process control using visible light and FTIR, respectively.
3) To provide specifically an integrated apparatus for monitoring the thickness and the photosensitivity of photoresist layers by using respectively, visible and ultraviolet spectrophotometry
4) To provide specifically an integrated apparatus for monitoring layers thickness and layers composition and for process control by using x-ray spectroscopy.
Hereinafter the term xe2x80x9coptical unitxe2x80x9d as used in the present invention means an assembly that includes all of the physical optical components that enables the performing of optical activities (e.g., measurements, image acquisition) at a specific spectral range, where the optical components comprise an illumination source, preferably external, a detector (e.g., spectrophotometer) or imaging device (e.g., area CCD) and a suitable combination of optical elements, such as lenses, beam splitters, mirrors, fiber optics and so on, for directing the input illumination beam toward the wafer and the output beam, from the wafer into the detector; The illumination source can be external to the measuring unit in which all the other components of the optical unit are assembled or can be installed within the measuring unit. In the first case the light beam is conveyed to the measuring unit by a suitable light guide.
The term xe2x80x9cchannelxe2x80x9d or xe2x80x9coptical channelxe2x80x9d as used in the present invention means the using of an xe2x80x9coptical unitxe2x80x9d for specific purpose and includes the communication with a control unit as well as electricity supply.
Thus, an xe2x80x9coptical unitxe2x80x9d can serve more than one xe2x80x9cchannelxe2x80x9d, as in the example above. In this example of the ITM NovaScan 210, channels 100 and 200 operating at visible light, comprise nearly the same optical components (except a spectrophotometer and a CCD) denoted for convenience as optical unit 4 (wherein the light source 10 is part of unit 4).
It is the object of the present invention to overcome the limitations of the prior art. The present invention relates to an integrated apparatus for monitoring wafers and for process control in the semiconductor manufacturing process, by means of optical measurements at more than one spectral range, and a method for use thereof. Said apparatus comprising at least two separate optical units, each for measurements at a different spectral range wherein each unit uses a different optical window.
The present invention further relates to a method for monitoring of wafers and for process control in the semiconductor manufacturing by optical measurements at more than one spectral range for any process in the semiconductor manufacturing and for the CVD process, in particular.
The apparatus according to the present invention comprises a measuring unit for performing optical measurements in predetermined sites on said wafer, illumination sources for illuminating said wafer via measuring unit, supporting means for holding, rotating and translating the wafer and a control unit connected to said measuring unit, to said supporting means and to said illumination sources. The measuring unit comprises: (a) at least two separate optical units, each operating at a different distinct spectral range; (b) a separate optical window for each optical unit through which the wafer is illuminated; (c) at least one movable optical head which includes part or all of the optical components of said optical units; (d) mechanical means for translating said optical head relatively to the wafer""s surface such that each of said optical units can measure the whole area of the wafer through its corresponding optical window and perform autofocusing. The apparatus, according to the present invention, can be installed inside any part of the semiconductor production line, i.e., inside the photocluster equipment, the chemical vapor deposition (CVD) equipment or the chemical mechanical polishing (CMP) equipment.
In a preferred embodiment of the present invention, one optical unit, comprising of optical elements suitable for measurements in the visible range, is used for positioning and for obtaining spectroscopic data in the visible range. The other optical unit or units consist of optical elements suitable for measurements at any other spectral ranges, such as the infrared, ultraviolet or X-ray or at a specific wavelength.
In a preferred embodiment of the present invention, said apparatus is installed inside the CVD equipment cluster and comprises two optical units. One optical unit, comprising of optical elements suitable for measurements in the visible range of the electromagnetic spectrum, is used for positioning and for thickness measurements. The second optical unit is for layer composition measurements and contamination analysis and comprises of optical components suitable for measurements in the infrared range of the spectrum based on Fourier Transform Infrared spectrometry (FTIR).
In another preferred embodiment of the present invention, the second unit comprises optical elements suitable for illumination and optical measurements in the ultraviolet range of the spectrum, is used for illuminating a wafer by ultraviolet illumination and measuring the reflected signals by means of a detector.
Yet in another preferred embodiment of the present invention, the second unit comprises optical elements suitable for illumination and optical measurements in the X ray range of the spectrum, is used for illuminating a wafer by X ray radiation and measuring the reflected signals by means of a detector.
In a preferred embodiment of the present invention the measuring unit comprises two adjacent elongated windows of length equal to or longer than a semiconductor wafer radius and separated by a distance d. The wafer is held by a stable support with means for rotating the wafer around an axis perpendicular to its plane. The movable optical head has means to move along the window length, and either the supporting means of the wafer or the movable optical head have means for linear translation along the x axis perpendicular to the windows elongated axis and equal to the distance xcex94x between the windows"" centers such that the wafer can be centered under one window or the other. This design of the windows, combined with the relative movements of wafer and optical head, enables each optical unit to measure any point on the surface of a wafer.
Yet, in another preferred embodiment of the present invention, the wafer""s supporting means has means for accurate rotation.
According to the present invention, there can be more than two optical units and corresponding windows, wherein the supporting means or the optical head have several positions or continuous translation with appropriate motion control along the x axis.